It’s a sunny day, and Vancouver’s Downtown Eastside neighborhood is buzzing. Commuters are commuting, delivery trucks are delivering, shopkeepers are shopkeeping. And on a half-acre garden surrounded by four busy streets, the city’s smallest workers are busy, too.

They’re bees, placed here by the nonprofit Hives for Humanity, a group that aims to build community through beekeeping. But the bees are doing more than making honey and facilitating friendships. They’re also monitoring the nearby area for pollution, with a little help from the Pacific Centre for Isotopic and Geochemical Research lab at the University of British Columbia.

There, lab director Dominique Weis and her team analyze the honey made by the bees in order to determine what’s in it.

«Honey is a representation of [pollution] sources in a hyperlocal environment,» says Kate Smith, a PhD student in Weis’s lab. «Bees drink water. They land on the soil. They pick up pollen.» And, of course, they drink nectar and make honey.

The project started three years ago when the founder of Hives for Humanity asked Weis if she could tell if the honey his bees were making was safe to eat. «Because she was being made fun of» for situating hives in a poor urban neighborhood instead of a more pristine, rural environment. Julia Common, the cofounder of Hives for Humanity along with her daughter, says “people were joking about finding heroin in the honey.” That was just a cruel joke, Common says, “but it got me thinking” about whether there might be anything else dangerous in the honey, such as lead from car and truck exhaust. She was introduced to Weis and the project took off.

Weis, Smith and her team, with help from Hives for Humanity, sampled about 30 hives for the pilot project. Apiarists use wooden coffee stirrers to scoop a bit of honey into a pre-cleaned container. They can’t use anything metal, because metal could contaminate the sample.

An apiarist uses a wooden coffee stirrer to sample honey from a frame in a beehive at Hastings Urban Farm.

(Courtesy K. Smith)

Weis, a geochemist who normally studies Hawaiian volcanoes, figured out how to convert the honey into a solution that can be analyzed. To do this, the honey needs to be dissolved in a solution, then heated to 7,000 Kelvin—hotter than the surface of the sun. Then it can be analyzed with a mass spectrometer, which measures trace amounts of elements, such as lead, cadmium or zinc.

Bees have been used as pollution monitors for decades. In its simplest form, they’re simply a canary in a coal mine: If a beehive is sickly or its bees die off, there’s probably some sort of pollution nearby. In recent years, monitoring-by-bee has gotten more sophisticated. The hive doesn’t need to suffer or die in order to provide valuable information.

Since bees visit thousands of flowers in a single day, usually in a tight radius of up to two miles around their hive, they both cover a lot of ground cheaply as well as provide a highly localized monitor. One must simply pop open a hive, harvest the honey and submit it to a battery of tests to know exactly what’s in the environment. Over the years, bees, honey and wax have been tested for fluoride, lead, zinc, nickel and potassium; more complicated molecules like naphthalene (a toxic compound derived from coal tar, and also the main ingredient in mothballs); even radioactive compounds like cesium, tritium and plutonium.

For the most part, the bees do a good job detecting chemicals. As long as you know «something about what kinds of substances are being looked for,» says Gene E. Robinson, director of the Carl R. Woese Institute for Genomic Biology and the Illinois Bee Research Facility, both at the University of Illinois, «the premise is very good.”

“What’s the chemistry? How might [the substances] interact with the … environment that you’re looking at?” he asks. For example, beeswax is a lipid, and many toxic chemicals are lipophilic, meaning they’re drawn to lipids. An experiment might turn up very little of a toxic substance in honey, even if it’s present in the wax, if the experimenter doesn’t know to also test the wax. Still, Robinson adds, the technique “can be very useful to magnify trace amounts of substances that [bees] encounter.”

Yet sometimes bee monitors turn up confusing results: In a three-year study at Los Alamos National Laboratory from 1994 to 1996, bees placed in hives around a radioactive waste lagoon known to contain six radioactive compounds showed consistent signs of contamination from four. The other two, tritium and sodium-22, «were all significantly different from each other» in each of the hives, possibly because the bees metabolize those elements differently from the others, study author Tim Haarmann wrote in a 2002 book chapter summarizing his results. Still, Haarmann concluded that «honey bees are indeed good indicators of radionuclide contamination when it is present in the environment.» Using that data for anything more specific, like tracking changes in the quantity of radiation over time, or pinpointing a specific source of radiation, remain a challenge.

Since 2006, bees have been tracking air pollution at Germany’s Frankfurt Airport, the fourth-busiest airport in Europe, and one with a new terminal currently under construction.

«Many people are opposed to the idea that the Frankfurt airport is getting bigger,» says Bernd Grunewald, director of the Bee Research Institute at the University of Frankfurt. «[The air traffic] creates a lot of problems for people living in the neighborhood of the airport.» The hives at the airport were meant to track whether air pollution from the jet engines—not to mention all the baggage tractors, de-icing trucks, and so on—could affect human health.

After 11 years of study, the team has troves of data on 16 chemicals, known as polycyclic aromatic hydrocarbons (PAHs), in honey, pollen and in moss. These PAHs mostly come from burning fossil fuels, especially at low temperatures (like when a jet engine is just warming up). Grunewald’s team chose these 16 because the U.S. EPA considers them «priority pollutants,» meaning they are regulated, and they are heavily studied. They’re also all thought to be toxic to human health in large enough quantities.

Unsurprisingly, the team found the presence of PAHs in the honey at the airport. But they also found nearly identical amounts of PAHs at their control site, a pristine area in the Taunus mountain range north of the city.

At least when it comes to PAHs, «the airport is as polluted or nonpolluted … as the supposed clean apiary,» Grunewald says.

Either that means that Germany’s jet engines are remarkably clean, or that PAHs are remarkably persistent. The latter explanation aligns well with a 2009 study from Italian scientists that found PAHs in honey and bees from hives near Rome’s Ciampino airport as well as hives in a nature reserve. These results «strengthen the supposition that PAHs show a wide distribution in the environment,» the authors wrote. In other words, maybe this pollution is just everywhere.

Common, the Hives for Humanity founder, actually believes that urban bees might have a better diet than rural bees—there are fewer pesticides and fungicides used in a city than in an agricultural area, and urban bees have a wide range of flowers to sip from, compared to agricultural bees that might only get to visit one type of crop.

The next step in all these experiments is to get more specific. If researchers can determine not just if pollutants are present in the environment but actually track their concentrations over time or trace them to the source, that would be a huge benefit. And that is what the UBC scientists hope to do.

«Everything on Earth has a unique isotopic fingerprint,» Weis says. «Lead from burning leaded gasoline has a unique isotopic signature. Lead from paint chips has a unique isotopic signature.” Some of the hives they’re studying are near the Port of Vancouver, which was the third busiest port in North America as of 2015, the most recent year statistics were available. Is air pollution from the port appearing in the honey? By carefully noting the isotopic signatures of all possible sources of pollution—a project that will take years—those sources can then be pinpointed inside the honey, giving Vancouverites a better idea of where pollution might be coming from and how to clear their air.

And as for the original question that started Weis down the path of studying honey? It’s safe. «We’re talking about tens of parts per billion [of lead], on the high end,» Weis says. «As far as consumption goes, there’s no cause for alarm, our instruments are just very, very sensitive.»